Thread: 355 cam choice

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Tech - those last heads and pistons you recommend would give an effective combustion chamber of 79cc right (72cc + 7cc)? Does your calculator give the dynamic CR with that combo?

I'm getting 8.75 DCR with my homegrown calculator with the cam intake closing at 36 degrees ABDC . . .

Originally Posted by SBC

Tech - those last heads and pistons you recommend would give an effective combustion chamber of 79cc right (72cc + 7cc)? Does your calculator give the dynamic CR with that combo?

I'm getting 8.75 DCR with my homegrown calculator with the cam intake closing at 36 degrees ABDC . . .

No, I have been using the Keith Black calculator for several years. I don't think it matters whose you use, as long as you stick to one calculator and know what kind of number it takes from that calculator to tolerate pump gas.

On the second line of post 19, you can see where I assumed 6cc's in the eyebrows. This would have been fairly accurate with a quality flat-top piston. I didn't have a clue as to what piston he had at the time I wrote that post, but was just swinging the bat through to see what we had. I further allotted 9cc's for the 0.040" gasket, so the entire volume would be 72 + 6 + 9 with a zero deck. If you figure an overbore of 0.030", you have 727cc's in the cylinder. 727+72+6+9=814. 72+6+9=87. 814 divided by 87=9.35:1 static compression ratio.

Using the KB calculator, if you enter 9.35, along with a 5.703" rod, 3.480" crank and 49 degree ABDC intake closing point (36 @ 0.050", advanced to 34 and with 15 added, which is what is called for by the calculator), you get a Dynamic Compression Ratio of 8.282:1, which is in the range of 8.00 to 8.30 that I shoot for on the KB calculator to tolerate pump gas.
http://www.kb-silvolite.com/calc.php?action=comp2

I just noticed that the KB piston I linked is actually 7cc's instead of 6cc's. There is probably 1 cc or more variance in the combustion chambers, so I'm gonna let it ride. It ain't rocket surgery.

Cool - I was wondering how the timing advance would affect everything and the 2 degrees alone wasn't making a big difference. The extra 15 degrees brings it into pump gas range as you said. THATS the factor that I haven't been considering.

Is there a rule of thumb as to how much timing can be added before everything is out of whack?? Seems like I have read posts suggesting as much as 36 degrees in some cases.

The main reason why on my build I am not using KB pistons is the design promotes carbon build up on the ring lands.Seems to be just a bad design.I spoke to Mahle some more to find you can run those pistons at 4.029 vs 4.030,one thousands tighter that limits or eliminates cold forge piston slap because of the coating.One tip they gave me was to NOT use anything like carb cleaner to clean the pistons before the install of them.That kind of cleaner lifts off the coating.Of course they are making claims the coating last for the long term where on another thread I had concerns posted.The piston/ring design on the Mahle hands down seal without any carbon build up.They also told me they don't build cast pistons or pistons without the coating.Yeah I think in this case I found the age old saying.............."You do get what you pay for".The Mahle of course costs more.

Originally Posted by 1gary

The main reason why on my build I am not using KB pistons is the design promotes carbon build up on the ring lands.Seems to be just a bad design.I spoke to Mahle some more to find you can run those pistons at 4.029 vs 4.030,one thousands tighter that limits or eliminates cold forge piston slap because of the coating.One tip they gave me was to NOT use anything like carb cleaner to clean the pistons before the install of them.That kind of cleaner lifts off the coating.Of course they are making claims the coating last for the long term where on another thread I had concerns posted.The piston/ring design on the Mahle hands down seal without any carbon build up.They also told me they don't build cast pistons or pistons without the coating.Yeah I think in this case I found the age old saying.............."You do get what you pay for".The Mahle of course costs more.

well that s BS there telling you.... must of been the broom pusher grab the phone ? i have used there cast piston that had NO coating on them and they do or did make pistons for PBM and they are not coated as i have used a set in a 355. botom line is how are you going to run a coat piston 001 less if you can not messure it for size real size?? its coated . if there 2618 there going to move if 4032 you can fit them closer to the wall for what your doing

Originally Posted by SBC

Is there a rule of thumb as to how much timing can be added before everything is out of whack?? Seems like I have read posts suggesting as much as 36 degrees in some cases.

I'm not sure what your're asking, but if you're talking about how much you should advance or retard a camshaft to get the characteristics of the motor where you want them, a rule of thumb there is that if you have to advance or retard more than 4 degrees, then you have chosen the wrong cam.

Originally Posted by SBC

Is there a rule of thumb as to how much timing can be added before everything is out of whack?? Seems like I have read posts suggesting as much as 36 degrees in some cases.

I'm not sure what your're asking, but if you're talking about how much you should advance or retard a camshaft to get the characteristics of the motor where you want them, a rule of thumb there is that if you have to advance or retard more than 4 degrees, then you have chosen the wrong cam.